On the dynamical state of galaxy clusters: insights from cosmological simulations II

Using a suite of cosmology simulations of a sample of $> 120$ galaxy clusters with $\log(M_{DM, vir}) \le 14.5$. We compare clusters that form in purely dark matter run and their counterparts in hydro runs and investigate 4 independent parameters, that are normally used to classify dynamical state. We find that the virial ratio $η$ in hydro-dynamical runs is $\sim 10$ per cent lower than in the DM run, and there is no clear separation between the relaxed and unrelaxed clusters for any parameter. Further, using the velocity dispersion deviation parameter $ζ$, which is defined as the ratio between cluster velocity dispersion $σ$ and the theoretical prediction $σ_t = \sqrt{G M_{total}/R}$, we find that there is a linear correlation between the virial ratio $η$ and this $ζ$ parameter. We propose to use this $ζ$ parameter, which can be easily derived from observed galaxy clusters, as a substitute of the $η$ parameter to quantify the cluster dynamical state.

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